U.S. patent number 5,112,610 [Application Number 07/586,690] was granted by the patent office on 1992-05-12 for method of making a natural sweetener based on stevia rebaudiana, and use thereof.
Invention is credited to Udo Kienle.
United States Patent |
5,112,610 |
Kienle |
May 12, 1992 |
Method of making a natural sweetener based on Stevia rebaudiana,
and use thereof
Abstract
A method of making a natural sweetener based on Stevia
rebaudiana includes extraction of plant parts of Stevia rebaudiana
with a solvent to provide an extract, and subjecting the extract to
an extraction with a supercritical gas to obtain an extraction
residue which is freed from undesired and taste-impairing
constituents.
Inventors: |
Kienle; Udo (7000 Stuttgart 70,
DE) |
Family
ID: |
6350984 |
Appl.
No.: |
07/586,690 |
Filed: |
September 24, 1990 |
Current U.S.
Class: |
426/548; 127/34;
536/18.1 |
Current CPC
Class: |
A23L
27/36 (20160801); A23L 27/11 (20160801); C07H
15/256 (20130101); Y02P 20/54 (20151101); Y02P
20/544 (20151101) |
Current International
Class: |
A23L
1/221 (20060101); A23L 1/236 (20060101); C07H
15/256 (20060101); C07H 15/00 (20060101); A61K
035/78 (); C07H 015/24 () |
Field of
Search: |
;424/195.1 ;536/18.1
;426/48,548 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0335265 |
|
Mar 1989 |
|
EP |
|
62-00496 |
|
Jan 1987 |
|
JP |
|
Other References
A I. Bakal & L. O'Brien Nabors, "Stevioside" in Alternative
Sweeteners, Marcel Dekker Inc., N.Y. 1986, pp. 295-307..
|
Primary Examiner: Griffin; Ronald W.
Assistant Examiner: Gitomer; Ralph
Attorney, Agent or Firm: Feiereisen; Henry M.
Claims
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims:
1. A method of making a natural sweetener substantially free of
bitter aftertaste from an extract obtained from plant parts of
Stevia rebaudiana; comprising the step of extracting said extract
with a supercritical gas to obtain an extraction residue.
2. A method as defined in claim 1 wherein the supercritical gas is
selected from the group consisting of carbon dioxide, ethane,
ethene, nitrous oxide, propane and propene.
3. A method as defined in claim 1 with the supercritical gas being
carbon dioxide and being at a temperature in the range of
31.degree. to 100.degree., at a pressure above 72.9 bar and at a
quantity, relative to the dry substance of the starting material
subjected to extraction, of 5 to 310 kg CO.sub.2 /kg dry
substance.
4. A method as defined in claim 3 wherein the temperature of the
supercritical carbon dioxide ranges between 50.degree. and
70.degree. and the pressure ranges between 100 and 400 bar, with
the quantity of supercritical carbon dioxide being in the range of
8 to 310 kg CO.sub.2 /kg dry substance.
5. A method as defined in claim 4 wherein the pressure of the
supercritical carbon dioxide ranges between 250 and 350 bar.
6. A method as defined in claim 1 wherein the extract is present in
form of a solution in an aqueous solvent.
7. A method as defined in claim 1 wherein the extract is present in
form of a solution in an organic solvent.
8. A method as defined in claim 1 wherein said step of extracting
the extract is performed in an extraction vessel filled with
packings, with the flow of supercritical gas being adjusted to the
supplied amount of extract in such a manner that the relative mass
ratio ranges between 5 to 50 kg CO.sub.2 /kg dry substance.
9. A method as defined in claim 8 wherein the mass ratio ranges
between between 8 to 50 kg CO.sub.2 /kg dry substance.
10. A method as defined in claim 1 wherein the extract subjected to
extraction with supercritical gas is aqueous.
11. A method as defined in claim 1 wherein the extract is solid and
in powder form, said extracting step being carried out at an
extraction temperature below 50.degree. C.
12. A method as defined in claim 1 wherein said extracting step is
carried out in the presence of an entrainer.
13. A method of making a natural sweetener from Stevia rebaudiana;
comprising the steps of:
providing as starting material plant parts of Stevia
rebaudiana;
extracting the plant parts with a solvent to provide an extract;
and
subjecting the extract to an extraction with a supercritical gas to
obtain an extraction residue.
14. A method of making a natural sweetener from Stevia rebaudiana;
comprising the steps of:
introducing as starting material plant parts of Stevia rebaudiana
in an extraction vessel; and
separating from the plant parts an extract by feeding a
supercritical gas into the extraction vessel so as to obtain an
extraction residue.
15. A method of making a natural sweetener from an extract obtained
form plant parts of Stevia rebaudiana; comprising the step of
extracting the extract with liquid carbon dioxide to obtain an
extraction residue.
16. A method as defined in claim 15 comprising extracting with
liquid carbon dioxide at a temperature ranging from 0.degree. to
31.degree. and at a pressure ranging from 40 to 72.9 bar.
17. A method as defined in claim 15 comprising extracting with
liquid carbon dioxide at a temperature ranging from 5.degree. to
31.degree..
18. A method of making a natural sweetener substantially free of
bitter aftertaste, from .alpha.-glycosylated stevioside or
rebaudiside A, comprising the step of extracting said
.alpha.-glycosylated stevioside or rebaudiside A with a
super-critical gas to obtain an extraction residue.
Description
BACKGROUND OF THE INVENTION
The invention refers to a method of making a natural sweetener
based on Stevia rebaudiana, and use thereof.
As set forth in the article entitled "Stevioside", page 295 to 307
by Abraham I. Bakal and Lyn O'Brien Nabors in the publication
"Alternative Sweeteners", Marcel Dekker Inc., New York 1986 as well
as in the various citations referred to in that article, the plant
Stevia rebaudiana is native in South America and is used as
traditional sweetener for mate tea. The components of this plant
are characterized by a high sweetness intensity so that tests were
undertaken to cultivate this plant not only in its native countries
but also in East Asia and to commercially exploit extracts obtained
therefrom. The sweetness of the plant parts and of the extracts
obtained therefrom can be attributed to a number of chemical
substances which all belong to the class of diterpene glycosides.
The most important singular compounds are the stevioside and
rebaudiside A which have the following chemical structure:
##STR1##
Aside from these two compounds, further compounds could be
identified which contribute to the sweetness intensity.
In order to make sweeteners from Stevia rebaudiana, the plant
parts, usually the dried leaves, are extracted with water or with
an organic solvent such as alcohol. The extracts are then subjected
to various refining steps for purifying and enrichment of the
components effecting the sweetness intensity. These refining steps
may encompass the following process types: precipitation of
contaminants by means of inorganic salts and subsequent treatment
of the extract with ion-exchangers, precipitation of the
contaminations through controlled variation of the pH value,
precipitation of undesired accompanying substances through
aggregation on polymers or fixed adsorbents, purification through
chromatographic steps, purification through adsorption on pigments;
liquid extraction; electrophoresis, membrane filtration.
The number of publications cited in Chemical Abstracts volumes
85-105, which primarily are published Japanese patent applications,
is above 70. Products which are obtained from raw extracts and have
improved sweetness intensity are also disclosed for example in the
U.S. Pat. Nos. 4,082,858 and 4,219,571, with the latter patent
specification referring to an enzymatic production method.
The sweetness intensity of the extract, which sometimes is simply
called "stevioside", is usually about 150 to 300 times the
sweetness intensity of sucrose depending on the used
concentration.
The reason that kept sweeteners derived from Stevia rebaudiana from
being introduced in Europe and North America is a bitter and
astringent aftertaste which frequently is also described as
menthol-like. In all known, commercially applicable methods, this
aftertaste remains in the extract and leaves a greatly impaired
taste, especially at high purity of the extract or at high
concentration. Although such taste or aftertaste has been tolerated
in countries in which sweeteners based on Stevia rebaudiana are
used in foodstuffs and beverages, a product of such quality would
not be accepted by consumers in Europe or North America. Further,
the bitter aftertaste also limits the application of sweeteners of
Stevia rebaudiana for use in alcohol-free beverages such as soft
drinks.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a natural
sweetener based on Stevia rebaudiana obviating the afore-stated
drawbacks.
In particular, it is an object of the present invention to provide
a natural sweetener on the basis of an extract obtained from plant
parts of Stevia rebaudiana without encountering an undesired
aftertaste, and yet retaining its full sweetness intensity.
These objects and others which will become apparent hereinafter are
attained in accordance with the present invention by separating
from the plant parts an extract through extraction with a solvent,
and extracting the extract with a supercritical gas for obtaining
an extraction residue which is freed from undesired and
taste-impairing constituents.
Through the provision of the method according to the present
invention, the undesired aftertaste is removed thus rendering the
obtained sweeteners applicable for a wide range of foodstuffs and
beverages, especially for soft drinks, and thence for products for
which extracts from Stevia rebaudiana were unsuitable to date. It
has been surprisingly found that the extraction with supercritical
gases attains a complete or nearly complete removal of those
components of Stevia rebaudiana which cause the bitter or
astringent aftertaste. This is also true for all commercially
available extracts or enzymatic transformation products.
None of the numerous citations discloses an extraction method with
supercritical gases, in particular with supercritical carbon
dioxide in order to remove the distasteful components of the Stevia
rebaudiana plant which not only are found in the leaves of Stevia
rebaudiana but also in all extracts and in the enzymatic
transformation products of stevioside.
It has further been found that the use of liquid carbon dioxide as
extractant can also provide an effective removal of the bitter and
astringent components of Stevia rebaudiana although the degree of
effectiveness of supercritical carbon dioxide is not attained.
The product obtained after extraction with supercritical gas i.e.
the extraction residue has a considerable improved taste. The field
of application is increased to such extent that higher sweetness
concentrations are attained, e.g. for soft drinks, without
diminishing the acceptance by the consumer.
A method of extraction with supercritical gases is known per se as
summarized in the publication by E. Stahl, K. W. Quirin, D. Gerard,
entitled "Verdichtete Gase zur Extraktion und Raffination",
Springer-Verlag, Berlin, Heidelberg, New York, London, Paris,
Tokyo, 1987 to which reference is made herewith.
The Japanese patent JP-A- 62-000496 discloses the attempt to
extract the sweetener stevioside from leaves of Stevia rebaudiana
with supercritical carbon dioxide. As set forth therein, the use of
supercritical carbon dioxide does not enable extraction of
stevioside unless 0.5 to 50 mol-% methanol, ethanol or acetone or a
tertiary mixture of supercritical carbon dioxide, water and
methanol is added. Stevioside obtained by such extraction is
contaminated by numerous undesirable constituents and especially
contaminated with taste-impairing components. For purposes of
purification, in particular purification of a conventionally
obtained stevioside extract, the extraction method with
supercritical carbon dioxide is not considered.
DETAILED DESCRIPTION
The method according to the present invention uses as extraction a
supercritical gas for refining stevia-extracts of all types. It has
been found that the desired results are attained when using a
number of gases although the individual gases differ in their
effectiveness to a certain degree. The removal of bitter and
astringent constituents of Stevia rebaudiana are better attained by
ethane, ethene, nitrous oxide, propane and propene than by carbon
dioxide or various hydrogen fluorides.
However, since organic extractants has commonly known drawbacks and
nitrous oxide supports the burning and thus must be handled with
great care, carbon dioxide has proven to be the preferred gas for
carrying out the method according to the present invention.
Modifications of the method according to the present invention,
especially the critical temperatures and pressures as well as
densities for the above-mentioned other extractants, are discussed
in the prior art publication (see e.g. the publication by E. Stahl
et al, as referred above, page 15). In contrast to the other
above-stated gases, carbon dioxide is physiologically safe,
non-combustible or explosive, not harmful to the environment and is
available in great amounts. Moreover, extraction methods using
supercritical carbon monoxide are well documented.
Carbon dioxide is raised to supercritical conditions (pressure
above 72.9 bar, temperature above 31.degree. C.) by a pressure
generator and raised to the extraction temperature isobarically by
means of a heat exchanger. Subsequently, the supercritical carbon
dioxide of desired temperature is fed in an extraction vessel
containing the raw material to be treated. At continuous process,
the supercritical carbon dioxide is led through the material being
extracted.
After extraction, the extract-laden gas is relaxed to a pressure
below 72.9 bar. The gas cools down and is present as wet steam,
with formation of a liquid extract-enriched phase and a gas
extract-enriched phase. For separation, the gas is vaporized and
isobarically brought to the temperature of separation, suitably
between 25.degree. and 50.degree. C. After separation, the
regenerated gas is cooled down to liquefaction temperature and
returned to the process.
Basically, the method according to the invention follows these
method steps. The temperature of extraction should be in the range
between 31.degree. C. and 100.degree. depending on the used
starting material. In order to attain an effective extraction of
the taste-impairing constituents, a sufficient mass rate of the
starting material being treated and the quantity of carbon dioxide
should be provided for.
It should be noted, however, that the temperature of extraction may
exceed 100.degree. C., provided an extract of Stevia rebauidiana is
used which is obtained with organic solvent boiling above
100.degree. C.
According to a further feature of the present invention, the
relative mass rate can be varied between 5 kg CO.sub.2 /kg starting
material and up to 310 kg CO.sub.2 /kg starting material.
Generally, the mass ratio lies between 8 kg CO.sub.2 /kg starting
material and 100 kg CO.sub.2 /kg starting material. A mass ratio
below 5 kg CO.sub.2 /kg starting material will not result in a
marked removal of undesired flavorings.
An optimal ratio of the relative mass rates at preferred conditions
of 60.degree. C. and 300 bar ranges between 8 and 100 kg CO.sub.2
/kg starting material.
When using liquid carbon dioxide, the temperatures may range from
0.degree. to 31.degree. C., preferably from 5.degree. to 31.degree.
C. and the pressures may range from 40 to 72.9 bar. The process
steps in case liquid carbon dioxide is employed as extractant are
similar to the process steps with supercritical carbon dioxide,
except there is no necessity of expanding the extract-laden
extraction to subcritical pressure.
The treatment of the starting material with carbon dioxide in a
manner as described herein results in a raffinate which can be
utilized as sweetener in soft drinks in suitable concentration
without impairment in taste. The sweetener has superior sweetness
properties in comparison to known synthetic sweeteners and is
characterized by a flavor profile which is similar to sugar
taste.
In the following, the method according to the invention will be
described in more detail by way of examples.
EXAMPLE 1
Treatment of Leaves of Stevia rebaudiana Bertoni
Whole or comminuted, fresh or dried leaves of Stevia rebaudiana
Bertoni are introduced in an extraction vessel. After sealing the
extraction vessel, supercritical carbon dioxide is fed through the
vessel for removing cuticle waxes, chlorophyll, other pigments and
especially taste-impairing components. The substances removed from
the leaves and solved in the supercritical carbon dioxide are
separated in the vessel to thereby regenerate the carbon dioxide
which can then be returned to the process after suitable
compression.
After ending the extraction process which takes about 8 hours, the
vessel is opened and the plant parts are withdrawn for direct use
or for subsequent aftertreatment in known manner like fresh or
dried leaves to thereby isolating the sweet diterpene glycosides
without impairment to the flavor.
This process, however, requires a great quantity of starting
material so that the use of leaves has shown to be less economical
even when increasing the bulk density of the dried or comminuted
leaves by pressing into pellets prior to the extraction.
Example 2
Treatment of Powder Extracts from Leaves of Stevia rebaudiana
Bertoni
A powdered extract, which is obtained from leaves of Stevia
rebaudiana Bertoni by conventional methods, is introduced in an
extraction vessel and treated with supercritical carbon dioxide. If
suitable, water, a C.sub.1 -C.sub.4 -alcohol or a suitable
hydrocarbon or a mixture of the above-mentioned solvents may be
added to the gas as entrainer.
Also in this case, the taste-impairing flavors are substantially
removed from the extraction residue which constitutes the sweetener
product. This type of treatment allows a removal of taste-impairing
components only to a lesser degree, and without employing
entrainers achieves not entirely satisfactory results. Moreover,
the thermal strain may also prove disadvantageous. In order to
avoid quality impairment, an extraction temperature of 50.degree.
C. should not be exceeded.
EXAMPLE 3
Treatment of Extract Solutions from Leaves of Stevia rebaudiana
Bertoni
Extract solutions containing an extract of leaves of Stevia
rebaudiana Bertoni in water or suitable alcohol or any other
suitable organic solvent or mixture of solvents are continuously
pumped in an extraction vessel which is filled with packings for
increasing the contact area between liquid and gas. The gas flow
and the addition of liquid extract are adjusted to each other in
such a manner that the relative mass flow in the extract solution
ranges between 8 and 50 kg CO.sub.2 /kg solids. Extraction pressure
and extraction temperature lie in the supercritical range, with
preferred condition being 300 bar and 60.degree. C.
An extraction method of this type is preferred and allows
substantial removal of taste-impairing components and other
contaminants. The purity of the liquid extract is not crucial, and
thus may be a crude extract, or may partly or completely be
purified by conventional methods, or an additional purification may
be provided after treatment in accordance with the present
invention.
When using as solvent an alcohol or an organic solvent, the extract
solutions should be aqueous and at least have a minimum water
content in order to allow the purified sweetener solved in an own
aqueous phase to be continuously withdrawn.
In case, extract solutions in alcoholic solvents or other organic
solvents are used, it is suitable to recover the solvent by known
methods for keeping the amount of solvent to be used to a
minimum.
In the event, the extract employed in the method according to the
present invention has a sufficiently high degree of purity
(sweetener content of more than 40%), the treated extract, i.e. the
extraction residue can be directly added in liquid form to
foodstuffs or beverages provided the solvent permits such
proceeding.
EXAMPLE 4
Purification of Raw Stevioside and Other Sweet Substances Isolated
from Stevia rebaudiana Bertoni as well as of Enzymatic
Transformation Products of Raw Stevioside
In a manner known per se, stevioside and rebaudiside A are
separated as pure substance from extracts of Stevia rebaudiana. The
substances are initially obtained in crystalline form as raw
stevioside and raw rebaudiside A which contain a number of
contaminants deposited upon the crystal surface and causing even in
this isolated form the taste-impairing characteristics as set forth
above.
In accordance with the present invention, for refining purposes,
the raw stevioside and the raw rebaudiside A is solved in a known
manner. The obtained solution is fed continuously in an extraction
vessel in a manner set forth in Example 3, with the taste-impairing
substances being removed as described in the previous examples. The
purified and taste-improved stevioside and rebaudiside A may be
added to the foodstuffs and beverages.
Likewise, solutions of raw stevioside which are enzymatically
transformed into rebaudiside A may be treated in accordance with
the method of the present invention for obtaining a taste-enhanced
natural sweetener. Raw stevioside may be enzymatically transformed
through various methods either into .alpha.-glycosylated Stevia
sweetener or into rebaudisine A. This is also true for
enzymatically transformed solutions of raw stevioside .alpha..
In order to be used in the field of food technology or by the end
consumer, the refined sweetener according to the present invention
may be prepared in various conventional manner. As previously set
forth, purified extract solutions may be directly added in liquid
form. It is, however, also feasible, to convert the purified
extracts or the purified stevioside or rebaudiside A into a solid
crystalline form and to make it commercially available in this
form. In view of its high sweetness intensity, stevia-extracts may
be suitably diluted with a tasteless diluent when being used by the
end consumer as sweetener for beverages such as tea or coffee. The
sweetener i.e. the Stevia-extract is suitably diluted with soluble
starch and commercially packed for distribution in small paper
bags, with a sweetness intensity comparable to one piece of lump
sugar.
While the invention has been illustrated and described as embodied
in a method of making a natural sweetener based on Stevia
rebaudiana, and use thereof, it is not intended to be limited to
the details shown since various modifications and structural
changes may be made without departing in any way from the spirit of
the present invention.
* * * * *